Two-step focus lens

ABSTRACT

A two-step focus lens for a digital camera so that the digital camera can switch between a close focal point and a distant focal point. The two-step focus lens includes a coil base, a sensor, and a lens base. The coil base has a coil which is wounded in a specific direction. The sensor drives the coil base to switch its two polarities according to the winding direction of the coil on the coil base. The lens base is movably installed inside the coil base and corresponds to the sensor. The end farther from the sensor has a magnetic component so that the lens base moves relative to the coil base to the close and distant focal points as the coil base switches its polarities.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a lens for digital cameras and, in particular,to a two-step focus lens.

2. Related Art

There are many ways to help people memorize happy times. Taking picturesis one of the most frequent ways. Therefore, one often needs to use acamera for recording the memorable moments. As we can see, the designsof cameras have evolved toward compact styles, so have the currentlypopular digital cameras. The focus structure of digital cameras can beroughly divided into a manual focus structure and an auto focusstructure. The manual focus structure allows one to focus the lens to adesired position, whereas the auto focus structure focuses on an objectby comparing with the image on an image sensor. The image sensor iseither a charge coupled device (CCD) sensor or a complementary metaloxide semiconductor (CMOS) sensor, and is controlled by a centralprocessing unit (CPU) installed inside the digital camera. In thebeginning, the lens moves back and forth around its original position(static position). As the lens moves, the CPU compares the image fromthe lens with the image in the image sensor. Finally, as the lens movesto the position where the image is the clearest, then the lens stops atthe position. In this case, the lens has to be continuously driven backand forth by an annular cam. The annular cam is provided with a lensdriving structure and driven to rotate by a stepping motor. At themoment when the CPU detects a clearest image as the lens moves back andforth, a stop signal is simultaneously sent to the lens. Therefore, thelens stops at the best focal position (static position). When the lensis to be moved back to the original position, the annular cam starts torotate again. Once the lens moves back to its original position, thephoto interrupter installed by the lens cylinder uses the shutter at theborder of the lens cylinder, to detect the original position of thelens. The shutter will interrupt the light of the penetration-type photointerrupter. The lens stops at the moment when the photo interrupterdetects the original position.

Consequently, the lens in a digital camera auto focus system has to bedriven continuously, so is the image detection. Every time an image iscaptured, the lens has to return to its original position. Thus, thelens focusing procedure is very time-consuming, which, in most of cases,results in losing the best image-capturing time. Moreover, the structureincluding a stepping motor, an annular cam, and a photo interrupter isvery expensive.

With reference to the cross-sectional view of a traditional digitalcamera auto focus structure in FIG. 1 and the correspondingthree-dimensional view in FIG. 2, when the stepping motor 1 receives astart signal from the digital camera CPU, it starts to rotate. Astepping motor gear 2 that matches with an annular cam gear 3 providedat the border of the annular cam 4 also rotates. The annular cam 4 thusstarts to rotate because of the stepping motor gear 2 and the annularcam gear 3. A position-detecting rod 5 moves back and forth (up anddown) along the slope surface of the annular cam 4. The whole lensmodule 6 moves back and forth along a track 7. One side of the lenscylinder is provided with a sheath, where the position-detecting rod 5is installed as one part and protrudes from the sheath. The outermostpart of the sheath of the lens module 6 is provided with a bearing 8moving back and forth along the track 7. The other side of the lens isprovided with a position-fixing fork 9 as one part of the lens cylinder.A position-fixing pin 10 is provided between the two terminals of theposition-fixing fork 9.

The bearing 8, the track 7, the position-fixing fork 9 and theposition-fixing pin 10 support the lens module 6. The lens module 6 isalways pressed toward an image sensor 11 by a coil spring 12, so thatthe tip of the position-detecting rod 5 always appropriately touches theslant surface of the annular cam 4. When the power of the digital camerais turned on, the image is formed on the image sensor 11 by the lensmodule 6. Once the switch of the auto focus structure is turned on, theimage focusing is transmitted to the CPU in a continuous way forchecking the image formed on the image sensor 11. When the image becomesclearest, the CPU sends out a stop-checking signal, and thestop-checking signal stops the stepping motor 1, releases the shutter,and captures the image. After these steps, the lens module 6 has toreturn to its original position (static position). A shutter-detectingblade 13 is provided at the edge of the annular cam 4. After capturingthe image, the annular cam 4 starts to rotate again to bring the lensmodule 6 back to its original position. When the shutter-detecting blade13 enters the slit of the photo interrupter 14, the beam in the photointerrupter 14 is interrupted by the shutter-detecting blade 13. Theannular cam 4 immediately stops here so that the lens module 6 canreturn and stop at its original position. As shown in FIG. 2, the lensmodule is right at its original position.

The lens module 6 has to move back and forth for the CPU to check theimage. This method of searching for an optimal focal point makes use ofmechanical and continuous lens motion to repeatedly check the image.Thus, it is time-consuming so that the user may miss the best timing.Moreover, this complicated structure has to be finely assembled andadjusted. Its components are often very expensive. Therefore, it wouldbe desirable to provide a simple structure that uses fewer cheapcomponents while saving focusing time, electric power, and the requiredspace.

SUMMARY OF THE INVENTION

An object of the invention is to provide a two-step focus lens thatutilizes a simple structure composed of fewer, cheaper components andsaves focusing time.

The disclosed two-step focus lens is used in a digital camera so thatthe digital camera can switch between a close focal point and a distantfocal point. The lens includes a coil base, a sensor, and a lens base.The coil base has a coil which is wounded in a specific direction. Thesensor drives the coil base to switch its two polarities according tothe winding direction of the coil on the coil base. The lens base ismovably installed inside the coil base and corresponds to the sensor.The end farther from the sensor has a magnetic component so that thelens base moves relative to the coil base to the close and distant focalpoints as the coil base switches its polarities. Hereinafter describesthe situation of the lens of the digital camera switching from its closefocal point to the distant focal point. The magnetism of the magneticcomponent on the lens base near the coil base is the same as that of thedistant end of coil base from the sensor when the lens is at its closefocal point position. A repelling force between the magnetic componentand the coil base is inducing. After the sensor switches the magneticpolarities of the coil base, the magnetism of the magnetic componentnear the coil base is different from that of the distant end of coilbase from the sensor. An attractive force between the magnetic componentand the coil base is inducing. Consequently, the lens moves to itsdistant focal point, and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the detaileddescription given hereinbelow illustration only, and thus are notlimitative of the present invention, and wherein:

FIG. 1 is a cross-sectional view of the auto focus structure in aconventional digital camera;

FIG. 2 is a three-dimensional view of the auto focus structure in aconventional digital camera;

FIG. 3 is an exploded view of the disclosed two-step focus lens;

FIG. 4 is an assembly diagram of the disclosed two-step focus lens; and

FIGS. 5A and 5B are cross-sectional views of the disclosed two-stepfocus lens in its close and distant focal points, respectively.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 shows an exploded view of the disclosed two-step focus lens. FIG.4 shows an assembly diagram of the disclosed two-step focus lens. FIGS.5A and 5B are cross-sectional views of the disclosed two-step focus lensin its close and distant focal points, respectively. The lens is used ina digital camera so that it can switch between its close and distantfocal points. The lens contains a coil base 20, a sensor 30, and a lensbase 40. The coil base 20 has a coil 21 which is wounded in a specificdirection. The sensor 30 drives the coil base 20 to switch its twopolarities according to the winding direction of the coil 21 on the coilbase 20. The lens base 40 is movably installed inside the coil base 20and corresponds to the sensor 30. The end of the lens base 40 fartherfrom the sensor 30 has a magnetic component 41, a stopper 42 and an arm43. The magnetic component 41 and the stopper 42 correspond to the innerrim of one end of the coil base 20 (this end is far from the sensor 30)so that the lens base 40 moves relative to the coil base 20 to the closeand distant focal points as the coil base 20 switches the polarities onits two ends. That is, the lens base 40 can only reach the stopper 42when it moves out relative to the coil base 20, and only reach themagnetic component 41 when it moves in. Without the electric powersupply, the arm provides a friction to keep the lens base 40 at itscurrent position.

Please refer to FIGS. 5A and 5B for the situation when the lens of thedigital camera switches from its close focal point to its distant focalpoint. When the lens is at its close focal point, the magnetism of themagnetic component 41 on the lens base 40 near the coil base 20 is thesame as that of the distant end of coil base 20 from the sensor 30. Arepelling force between the magnetic component 41 and the coil base 20is inducing. After the sensor 30 switches the magnetic polarities of thecoil base 20, the magnetism of the magnetic component 41 near the coilbase 20 is different from that of the distant end of coil base 20 fromthe sensor 30. Thus, an attractive force between the magnetic component41 and the coil base 20 is inducing. Consequently, the lens moves to itsdistant focal point.

Since the arm 43 can provide a friction, no electric power is neededafter the sensor 30 moves the lens base 40 to the close or distant focalpoint. The arm 43 directly provides the necessary friction between thelens base 40 and the inner surface of the coil base 20. So the frictionfixes the lens base 40 at its close or distant focal point.

Please further refer to FIGS. 5A and 5B for the situation when the lensof the digital camera switches from its distant focal point to its closefocal point. When the lens is at its distant focal point, the magnetismof the magnetic component 41 on the lens base 40 near the coil base 20is different from that of the distant end of coil base 20 from thesensor 30. An attractive force between the magnetic component 41 and thecoil base 20 is inducing. After the sensor 30 switches the magneticpolarities of the coil base 20, the magnetism of the magnetic component41 near the coil base 20 is the same as that of the distant end of coilbase 20 from the sensor 30. A repelling force between the magneticcomponent 41 and the coil base 20 is inducing. Consequently, the lensmoves to its close focal point.

Since the arm 43 can provide a friction, no electric power is neededafter the sensor 30 moves the lens base 40 to the close or distant focalpoint. The arm 43 directly provides the necessary friction between thelens base 40 and the inner surface of the coil base 20. So the frictionfixes the lens base 40 at its close or distant focal point.

Based upon the above description, one sees that the invention uses avery simple structure that involves fewer inexpensive components toachieve the goal of short focusing time.

Certain variations would be apparent to those skilled in the art, whichvariations are considered within the spirit and scope of the claimedinvention.

1. A two-step focus lens used in a digital camera for the digital camera to switch between a close focal point and a distant focal point, comprising: a coil base having a coil which is wounded in a specific direction; a sensor driving the coil base to switch the magnetic polarities of its two ends according to the winding direction of the coil on the coil base; and a lens base which is movably installed inside the coil base and which is corresponding to the sensor, and the lens base has the distant end from the sensor is provided with a magnetic component so that the lens base moves relative to the coil base between a close focal point and a distant focal point as the coil base switches the magnetic polarities of its two ends.
 2. The two-step focus lens of claim 1, wherein the lens base is further provided with a stopper which is along with the magnetic component corresponding to the inner rim of one end of the coil base, so that the lens base only reaches the stopper as it moves out relative to the coil base and the lens base only reaches the magnetic component as its moves in relative to the coil base.
 3. The two-step focus lens of claim 1, wherein the lens base is further provided with an arm to provide a friction that keeps the lens base at its current position. 